Forest is also calling for greater freedom for patients, visitors and staff who want to smoke cigarettes at hospitals.

Freedom of Information requests were made to 200 NHS trusts in England by the organisation, 170 of which provided a response.

Around 45% said they allowed e-cigarettes to be used outside in 2018 and 11% of trusts, mainly specialising in mental health, permitted vaping indoors, the research found.

However 14% said they were planning to amend their policies in 2019 to allow vaping outside buildings, in shelters or in wards.

Forest said vaping should be permitted in all outdoor areas at hospitals and inside buildings and on wards if management considers it appropriate.

More than three-quarters (76%) of NHS trusts said they did not allow cigarettes to be smoked anywhere on hospital grounds and only one in five (22%) provide smoking shelters, the research also found.

Meanwhile a third (32%) of trusts said they had installed a button which triggers a recorded message when pressed by a member of the public or staff, to help deter smokers.

Forest described the devices as "shame-a-smoker buttons".

"We welcome the fact that some trusts are reviewing their policies on the use of e-cigarettes, but adopting a more sensible approach to vaping shouldn't come at the price of a complete ban on smoking," Simon Clark, director of Forest, said.

"Banning smoking on hospital grounds demonstrates a staggering lack of compassion for smokers who may be stressed, upset and in need of a comforting cigarette.